Solid-oxide fuel cell system having an integrated reformer and waste energy recovery system

ABSTRACT

A solid-oxide fuel cell system including an integrated reforming unit comprising a hydrocarbon fuel reformer; an integral tail gas and cathode air combustor and reformer heat exchanger; a fuel pre-heater and fuel injector cooler; a fuel injector and fuel/air mixer and vaporizer; a reforming air pre-heating heat exchanger; a reforming air temperature control valve and means; and a pre-reformer start-up combustor. The integration of a plate reformer, tail gas combustor, and combustor gas heat exchanger allows for efficient operation modes of the reformer, both endothermic and exothermic as desired. The combustor gas heat exchanger aids in temperature regulation of the reformer and reduces significant thermal gradients in the unit.

TECHNICAL FIELD

[0001] The present invention relates to hydrogen/oxygen fuel cellshaving a solid-oxide electrolytic layer separating an anode layer from acathode layer; more particularly, to fuel cell assemblies and systemscomprising a plurality of individual fuel cells in a stack wherein airand reformed fuel are supplied to the stack; and most particularly, tosuch a fuel cell system including an on-board hydrocarbon reformer andwaste energy recovery assembly including a spent fuel combustor and heatexchangers.

BACKGROUND OF THE INVENTION

[0002] Fuel cells which generate electric current by the electrochemicalcombination of hydrogen and oxygen are well known. In one form of such afuel cell, an anodic layer and a cathodic layer are separated by anelectrolyte formed of a ceramic solid oxide. Such a fuel cell is knownin the art as a “solid oxide fuel cell” (SOFC). Hydrogen, either pure orreformed from hydrocarbons, is flowed along the outer surface of theanode and diffuses into the anode. Oxygen, typically from air, is flowedalong the outer surface of the cathode and diffuses into the cathode.Each O₂ molecule is split and reduced to two O⁻² anions catalytically bythe cathode. The oxygen anions transport through the electrolyte andcombine at the anode/electrolyte interface with four hydrogen ions toform two molecules of water. The anode and the cathode are connectedexternally through a load to complete the circuit whereby four electronsare transferred from the anode to the cathode. When hydrogen is derivedby “reforming” hydrocarbons such as gasoline in the presence of limitedoxygen, the “reformate” gas includes CO which is converted to CO₂ at theanode via an oxidation process similar to that performed on thehydrogen. Reformed gasoline is a commonly used fuel in automotive fuelcell applications.

[0003] A single cell is capable of generating a relatively small voltageand wattage, typically between about 0.5 volt and about 1.0 volt,depending upon load, and less than about 2 watts per cm² of cellsurface. Therefore, in practice it is known to stack together, inelectrical series, a plurality of cells. Because each anode and cathodemust have a free space for passage of gas over its surface, the cellsare separated by perimeter spacers which are selectively vented topermit flow of gas to the anodes and cathodes as desired but which formseals on their axial surfaces to prevent gas leakage from the sides ofthe stack. The perimeter spacers may include dielectric layers toinsulate the interconnects from each other. Adjacent cells are connectedelectrically by “interconnect” elements in the stack, the outer surfacesof the anodes and cathodes being electrically connected to theirrespective interconnects by electrical contacts disposed within thegas-flow space, typically by a metallic foam which is readilygas-permeable or by conductive filaments. The outermost, or end,interconnects of the stack define electric terminals, or “currentcollectors,” which may be connected across a load.

[0004] A complete SOFC system typically includes auxiliary subsystemsfor, among other requirements, generating fuel by reforminghydrocarbons; tempering the reformate fuel and air entering the stack;providing air to the hydrocarbon reformer; providing air to the cathodesfor reaction with hydrogen in the fuel cell stack; providing air forcooling the fuel cell stack; providing combustion air to an afterburnerfor unspent fuel exiting the stack; and providing cooling air to theafterburner and the stack. There typically are many gas conduitconnections between components in the system. These connectionstypically are conveying high temperature oxidant gas (air and exhaust)or hydrogen-rich reformate fuel at high temperature. Conventionalapproaches for conveying these gases include plumbing networkscomprising metal tubing, pipes, and fittings. These components oftenhave welded or compression-fitting connections that have the undesirablecharacteristics of high cost, large size, complexity, and moderatereliability. Typically, each component is directed to a specificfunction without regard to an overarching system architecture andphysical consolidation.

[0005] What is needed is a means for reducing the complexity, cost, andsize of a solid-oxide fuel cell system by consolidating the auxiliarysystems, piping, and connections.

[0006] It is a principal object of the present invention to simplify theconstruction and reduce the cost and size of a solid-oxide fuel cellsystem.

[0007] It is a further object of the invention to increase thereliability and safety of operation of such a fuel cell system.

BRIEF DESCRIPTION OF THE INVENTION

[0008] Briefly described, in a solid-oxide fuel cell system, a compact,highly space-efficient fuel/air manifold assembly conveys hightemperature air, exhaust, and hydrogen-rich fuel such as, for example,reformate or pure hydrogen, to and from the core components of thesystem. The manifold is a three-dimensional assembly of plates andshallow partitioned elements which are easily and inexpensively formed.When assembled, the manifold comprises a network of passageways whichallow for the mounting, close-coupling, and integration of critical fuelcell system components. An integrated fuel reformer partially oxidizesliquid hydrocarbon fuel catalytically into hydrogen and carbon monoxideand interacts via heat exchangers to controllably add or subtract heatin various gas flows in the system. An integrated air supply systempressurizes atmospheric air to provide oxygen for the fuel cellreaction, both through and controllably bypassing cathode air heatexchangers; to provide combustion air for a combustor of tail gas fromthe anodes; and to provide air to a liquid fuel vaporizer integral withthe reformer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] These and other features and advantages of the invention will bemore fully understood and appreciated from the following description ofcertain exemplary embodiments of the invention taken together with theaccompanying drawings, in which:

[0010]FIG. 1 is a schematic cross-sectional view of a two-cell stack ofsolid oxide fuel cells;

[0011]FIG. 2 is a schematic mechanization diagram of an SOFC system inaccordance with the invention;

[0012]FIG. 3 is an isometric view from above of a two-stack fuel cellassembly, shown connected electrically in series between two currentcollectors;

[0013]FIG. 4 is an isometric view like that shown in FIG. 3, with acover enclosing the stacks;

[0014]FIG. 5 is an elevational cross-sectional view taken along line 5-5in FIG. 4;

[0015]FIG. 6 is an elevational cross-sectional view taken along line 6-6in FIG. 4;

[0016]FIG. 7 is an equatorial cross-sectional view taken along line 7-7in FIG. 4;

[0017]FIG. 8 is an isometric view from above, showing a fuel cellassembly comprising the apparatus of FIG. 4 mounted on a manifold inaccordance with the invention, along with reforming, combusting, andheat exchanging apparatus for servicing the fuel cell stacks;

[0018]FIG. 9 is an isometric view from above, showing the fuel cellassembly of FIG. 8 mounted in the lower element of a thermal enclosure;

[0019]FIG. 10 is an isometric view from above of an air supply assemblyfor controllably providing air to the fuel cell assembly shown in FIGS.8 and 9;

[0020]FIG. 11 is an exploded isometric view of a fuel cell system inaccordance with the invention, showing the air supply assembly of FIG.10 disposed in a structural enclosure, and showing the fuel cellassembly of FIG. 9 fully enclosed by both upper and lower elements of athermal enclosure;

[0021]FIG. 12 is an isometric view from above of a fully assembled fuelcell system in accordance with the invention;

[0022]FIG. 13 is an exploded isometric view from the front, showing amulti-element basal manifold in accordance with the invention fordistributing air and reformate fuel and exhaust products through andaround the fuel cell stacks, as shown in FIG. 8;

[0023]FIG. 14 is an isometric view from the rear, showing the manifoldof FIG. 13 partially assembled;

[0024]FIG. 15 is an isometric view from the rear, showing the manifoldof FIG. 13 further assembled;

[0025]FIG. 16 is a plan view of the lower level of chambers formed bythe lower two elements shown in FIG. 13;

[0026]FIG. 17 is a plan view of the upper level of chambers formed bythe third and fourth elements shown in FIG. 13;

[0027]FIG. 18 is a plan view of the uppermost element shown in FIG. 13,showing the mounting surface for the apparatus shown in FIG. 8.

[0028]FIG. 19 is an isometric view from above of a fuel reformer andwaste energy recovery (reforWER) system in accordance with theinvention;

[0029]FIG. 20 is an isometric view from above of an elevationallongitudinal section of the reforWER system shown in FIG. 19;

[0030]FIG. 21 is a plan view of a first horizontal section of thereforWER system shown in FIG. 19, showing the path of fuel reformationthrough the system;

[0031]FIG. 22 is a plan view of a second horizontal section of thereforWER system shown in FIG. 19, showing the path of combustor exhaustand exchange of heat through the system;

[0032]FIG. 23 is a detailed isometric view from above of an airdistribution manifold assembly shown in FIG. 10; and

[0033]FIG. 24 is a horizontal cross-sectional view through the manifoldshown in FIG. 23.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Referring to FIG. 1, a fuel cell stack 10 includes elements knownin the art of solid-oxide fuel cell stacks comprising more than one fuelcell. The example shown includes two identical fuel cells 11, connectedin series, and is of a class of such fuel cells said to be“anode-supported” in that the anode is a structural element having theelectrolyte and cathode deposited upon it. Element thicknesses as shownare not to scale.

[0035] Each fuel cell 11 includes an electrolyte element 14 separatingan anodic element 16 and a cathodic element 18. Each anode and cathodeis in direct chemical contact with its respective surface of theelectrolyte, and each anode and cathode has a respective free surface20,22 forming one wall of a respective passageway 24,26 for flow of gasacross the surface. Anode 16 of one fuel cell 11 faces and iselectrically connected to an interconnect 28 by filaments 30 extendingacross but not blocking passageway 24. Similarly, cathode 18 of fuelcell 11 faces and is electrically connected to interconnect 28 byfilaments 30 extending across but not blocking passageway 26. Similarly,cathode 18 of a second fuel cell 11 faces and is electrically connectedto a cathodic current collector 32 by filaments 30 extending across butnot blocking passageway 26, and anode 16 of fuel cell 11 faces and iselectrically connected to an anodic current collector 34 by filaments 30extending across but not blocking passageway 24. Current collectors32,34 may be connected across a load 35 in order that the fuel cellstack 10 performs electrical work. Passageways 24 are formed by anodespacers 36 between the perimeter of anode 16 and either interconnect 28or anodic current collector 34. Passageways 26 are formed by cathodespacers 38 between the perimeter of electrolyte 14 and eitherinterconnect 28 or cathodic current collector 32. Anode spacer 36 andcathode spacer 38 are formed from sheet stock in such a way as to yieldthe desired height of the anode passageways 24 and cathode passageways26.

[0036] Preferably, the interconnect and the current collectors areformed of an alloy, typically a “superalloy,” which is chemically anddimensionally stable at the elevated temperatures necessary for fuelcell operation, generally about 750° C. or higher, for example,Hastelloy, Haynes 230, or a stainless steel. The electrolyte is formedof a ceramic oxide and preferably includes zirconia stabilized withyttrium oxide (yttria), known in the art as YSZ. The cathode is formedof, for example, porous lanthanum strontium manganate or lanthanumstrontium iron, and the anode is formed of, for example, a mixture ofnickel and YSZ.

[0037] In operation (FIG. 1), reformate gas 21 is provided topassageways 24 at a first edge 25 of the anode free surface 20, flowsparallel to the surface of the anode across the anode in a firstdirection, and is removed at a second and opposite edge 29 of anodesurface 20. Hydrogen and CO diffuse into the anode to the interface withthe electrolyte. Oxygen 31, typically in air, is provided to passageways26 at a first edge 39 of the cathode free surface 22, flows parallel tothe surface of the cathode in a second direction which can be orthogonalto the first direction of the reformate (second direction shown in thesame direction as the first for clarity in FIG. 1), and is removed at asecond and opposite edge 43 of cathode surface 22. Molecular oxygen gas(O₂) diffuses into the cathode and is catalytically reduced to two O⁻²anions by accepting four electrons from the cathode and the cathodiccurrent collector 32 or the interconnect 28 via filaments 30. Theelectrolyte ionically conducts or transports O⁻² anions to the anodeelectrolyte innerface where they combine with four hydrogen atoms toform two water molecules, giving up four electrons to the anode and theanodic current collector 34 or the interconnect 28 via filaments 30.Thus cells 11 are connected in series electrically between the twocurrent collectors, and the total voltage and wattage between thecurrent collectors is the sum of the voltage and wattage of theindividual cells in a fuel cell stack.

[0038] Referring to FIG. 2, a schematic mechanization diagram of asolid-oxide fuel cell system 12 in accordance with the inventionincludes auxiliary equipment and controls.

[0039] A conventional high speed inlet air pump 48 draws inlet air 50through an air filter 52, past a first MAF sensor 54, through a sonicsilencer 56, and through a cooling shroud 58 surrounding pump 48.

[0040] Air output 60 from pump 48, at a pressure sensed by pressuresensor 61, is first split into branched conduits between a feed 62 and afeed 72. Feed 62 goes as burner cooling air 64 to a tail gas afterburner66 having an igniter 67 via a second MAF sensor 68 and a burner cool aircontrol valve 70.

[0041] Feed 72 is further split into branched conduits between an anodeair feed 74 and a cathode air feed 75. Anode feed 74 goes to ahydrocarbon fuel vaporizer 76 via a third MAF sensor 78 and reformer aircontrol valve 80. A portion of anode air feed 74 may be controllablydiverted by control valve 82 through the cool side 83 of reformatepre-heat heat exchanger 84, then recombined with the non-temperedportion such that feed 74 is tempered to a desired temperature on itsway to vaporizer 76. Downstream of vaporizer 76 is a start-up combustor77 having an igniter 79. During start-up, when the reformer is cold orwell below operating temperature, vaporized fuel is ignited in combustor77 and the burned gas is passed directly through the reformer to warmthe plates therein more rapidly. Obviously, the start-up combustor isdeactivated during normal operation of the system.

[0042] Cathode air feed 75 is controlled by cathode air control valve 86and may be controllably diverted by cathode air preheat bypass valve 88through the cool side 90 of cathode air pre-heat heat exchanger 92 onits way to stacks 44,46. After passing through the cathode sides of thecells in stacks 44,46, the partially spent, heated air 93 is fed toburner 66.

[0043] A hydrocarbon fuel feed pump 94 draws fuel from a storage tank 96and delivers the fuel via a pressure regulator 98 and filter 100 to afuel injector 102 which injects the fuel into vaporizer 76. The injectedfuel is combined with air feed 74, vaporized, and fed to a reformercatalyst 104 in main fuel reformer 106 which reforms the fuel to,principally, hydrogen and carbon monoxide. Reformate 108 from catalyst104 is fed to the anodes in stacks 44,46. Unconsumed fuel 110 from theanodes is fed to afterburner 66 where it is combined with air supplies64 and 93 and is burned. When gases are below self-ignition temperature,they are ignited by igniter 67. The hot burner gases 112 are passedthrough a cleanup catalyst 114 in main reformer 106. The effluent 115from catalyst 114 is passed through the hot sides 116,118 of heatexchangers 84, 92, respectively, to heat the incoming cathode and anodeair. The partially-cooled effluent 115 is fed to a manifold 120surrounding stacks 44,46 from whence it is eventually exhausted 122.

[0044] Still referring to FIG. 2, a first check valve 150 and a firstoxygen getter device 124 are provided in the conduit feeding reformate108 to the anodes (not visible) in stacks 44,46. A second check valve152 and second oxygen getter device 126 are similarly provided in theconduit feeding spent reformate 110 from the anodes to afterburner 66.As described above, during cool-down of the fuel cell stacks aftershut-down of the assembly, it is important to prevent migration ofoxygen into anode passages 24 wherein anode surface 20, comprisingmetallic nickel, would be subject to damaging oxidation. Each checkvalve includes a typical frusto-conical valve seat 154 receptive of avalve ball 156. Preferably, each valve 150,152 is oriented withinassembly 12 such that the ball is held in the seat by gravity whenreformate is flowed through the system in the forward direction. Thus,fuel flow opens the valve sufficiently for fuel to pass in the forwarddirection. When assembly 12 is shut down, each valve is closed bygravity. The valves may not be identical, as oxygen flows opposite tothe reformate in valve 152, but in the same direction as the reformatein valve 150; the so the balls and seats may require different weightsand/or sizes to function as intended. Each getter 124,126 includes apassageway 128 having an inlet 130 and an outlet 132 through whichreformate is passed during operation of the fuel cell assembly. Withinthe passageway is a readily-oxidized material 134 (oxygen-reducingmeans), for example, nickel metal foam, nickel wire or nickel mesh,which is capable of gettering oxygen by reaction therewith but whichdoes not present a significant obstruction to flow of reformate throughthe passageway. Nickel in the getters reacts with oxygen to producenickel oxide, NiO, when the assembly is shut down, thus protecting thenickel-containing anodes from oxidation. When the assembly is turnedback on, reformate is again produced which, in passing through thegetters, reduces the NiO back to metallic nickel, allowing the gettersto be used repeatedly.

[0045] Still referring to FIG. 2, three-way control valve 160 isdisposed in line 93 conveying spent cathode air from the stacks 44,46 tocombustor 66. To control combustion temperature in combustor 66 bycontrolling air volume sent thereto, a portion of spent cathode air maybe bypassed around the combustor and diverted into the combustor exhauststream downstream of heat exchanger 84. If the mixture in the combustoris relatively rich in fuel, as may happen during start-up, thecombustion temperature can be high enough to generate undesirable oxidesof nitrogen and/or damage the combustor components. If the mixture isrelatively lean in fuel, the resulting combustion temperature can be toolow for supporting an endothermic reforming reaction, or can causereduced efficiency in the cathode pre-heat heat exchanger 92.

[0046] For clarity of presentation and to enhance the reader'sunderstanding, the numbers of elements of the invention as presentedfurther below are grouped in century series depending upon thefunctional assembly in which the elements occur; therefore, elementsrecited above and shown in FIGS. 1 and 2 may have different numericaldesignators when shown and discussed below, e.g., stacks 44,46 becomestacks 344,346.

[0047] Referring to FIGS. 3 through 7, in a fuel cell stack assembly 300in accordance with the invention, the cells 311 are arrangedside-by-side and may comprise a plurality of cells 311, respectively,such that each of first stack 344 and second stack 346 is a stack ofidentical fuel cells 311. The plurality of cells is preferably about 30in each of the two stacks. The cells 311 in stack 344 and stack 346 areconnected electrically in series by interconnect 347, and the stacks areconnected in series with cathode current collector 332 and anode currentcollector 334 on the bottom of the stacks. The current collectors aresized to have a “footprint” very close to the same dimension as acover-sealing flange 340. The current collectors preferably areadhesively sealed to a stack mounting plate 338, and the stackspreferably are in turn adhesively sealed to the current collectors. Thesealing flange 340 for the cover 342 and top 343 is then mounted andsealed to the current collector plates. A gasket 341 between flange 340and the current collectors is a dielectric so that flange 340 does notcause a short between the current collectors. Power leads 350,352 areattached to current collectors 332,334, respectively, through strong,reliable and highly conductive metallurgical bonds, such as brazing. Inthis manner, the current collectors may pass under the cover mountingflange 340, with no additional sealing or power lead attachmentrequired, and do not have to pass undesirably through the cover itself,as in some prior art stack assemblies. Passing leads through the covermakes the assembly more complex and less reliable.

[0048] Referring to FIG. 8, a fuel cell assembly 400 in accordance withthe invention comprises stack assembly 300 operatively mounted on anintegrated fuel/air manifold assembly 500 which also supports first andsecond cathode air heat exchangers 600 and an integrated fuel reformerand waste energy recovery unit (“reforWER”) 1100. Assembly 400 receivesair from air supply system 900 (FIGS. 10-12) as described below andselectively preheats air going to the reformer. ReforWER 1100 reformshydrocarbon fuel, such as gasoline, into reformate fuel gas comprisingmostly hydrogen, carbon monoxide, and lower-molecular weighthydrocarbons, tempers the air and reformate entering the stacks,selectively burns fuel not consumed in the stacks, recovers heat energygenerated in various internal processes which would otherwise be wasted,and exhausts spent air and water, all in order to efficiently generateDC electric potential across power leads 350,352 (not visible in FIG.8). The structure and internal functioning of reforWER 1100 is discussedin detail hereinbelow.

[0049] Referring to FIGS. 9 and 11, there are two basic functions forthe enclosure of a fuel cell system. The first is to provide thermalinsulation for the components which function at an elevated temperature(700-900° C.) to maintain them at that temperature for efficientoperation, to protect lower temperature components, and to reduce theexterior temperature over the overall unit to a human-safe level. Thesecond is to provide structural support for mounting of individualcomponents, mounting the system to another structure such as a vehicle,protection of the internal components from the exterior environment, andprotection of the surrounding environment from the high temperatures ofthe fuel cell assembly. Prior art systems utilize a single enclosure toprovide all functions, which can be complex and costly to fabricate andassemble, and consumptive of space.

[0050] Still referring to FIGS. 9 and 11, in the present invention,enclosure of the fuel cell assembly comprises two nested enclosures: athermal enclosure 700 and a structural enclosure 800. Fuel cell assembly400 is first disposed in a “clam-shell” type thermal enclosure 700,comprising a bottom portion 702 and a top portion 704, which in turn isdisposed in a structural enclosure 800. The split line 706 betweenbottom portion 702 and top portion 704 is easily arranged such that allpipes, manifolds, shafts, power leads, etc., which need to pass betweenthe “hot zone” 716 within the thermal enclosure and the “cool zone” 816within the structural enclosure, do so in the middle of split line 706.This provides for easy assembly of the hot components into the thermalenclosure. First, all hot zone components, included in assembly 400, arenestled into in bottom portion 702, which may be provided with aconforming well 708 for securely holding and cushioning assembly 400, asshown in FIG. 9. The mating surface 710 of bottom portion 702, alongsplit line 706, is configured as required to accommodate the lowerhalves of the components extending through enclosure 700. Top portion704 is configured to matingly engage bottom portion 702. Top portion 704is placed onto bottom portion 702 and may be sealed thereto along line706 as desired. Thermal enclosure 700 may be formed of any suitablehigh-temperature high-efficiency insulating material, as is known in theinsulating art, and may be a composite including a light-weight metalcase. The range of suitable insulating materials is expanded by removingthe constraint of overall structural integrity afforded by providing aseparate structural enclosure 800.

[0051] Structural enclosure 800 preferably is fabricated from thickermetal, for example, to provide structural strength and a simple shape,such as a box with a removable lid, for ease of fabrication. Featuressuch as brackets, studs, electrical connectors, studs, weld-nuts, airintake ducts, and exhaust ducts, for example, may be part of thestructural enclosure for mounting internal components thereto and forconnecting the system to external structures. Features for vibration andshock isolation (not shown) may also be provided with the enclosure.

[0052] The air control assembly 900 is connected to elements of fuelcell assembly 400 projecting through split line 706; and assemblies700,900 are then installed within structural enclosure 800, as shown inFIG. 12, to form a fuel cell system 1000 in accordance with theinvention. Preferably, control system 200 (shown schematically in FIG. 2as power conditioner 202, circuit protection I/O 204, drivers 206, andelectronic control unit 208, but not visible in FIG. 12) is alsoinstalled onboard the system within cool zone 816 to minimize the numberof discrete signals 210 which must be passed through enclosure 800 viaconnector 820. Note also that high current capacity power leads alsopass through enclosure 800 via dual connectors 821.

[0053] Referring to FIGS. 13 through 18, an integrated fuel/air manifoldassembly 500 receives air via flexible bellows elements from air supplyassembly 900 and reformed fuel from reforWER assembly 1100 and conveyshigh temperature air, exhaust, and hydrogen-rich reformate fuel to andfrom the core components of the system. Basal manifold assembly 500 isshown in FIG. 13 as comprising a three-dimensional assembly of threeperforated plates and two partitioned elements which are easily andinexpensively formed and which comprise a two-level network ofpassageways which allow for the mounting, close-coupling, andintegration of critical fuel cell system components, including heatexchangers, combustors, fuel reformers, solid-oxide fuel cell stacks,check valves, threaded inserts, and catalyzed and non-catalyzed filters.Of course, while a five-component manifold is shown for simplicity,within the scope of the invention any two of the perforated platesobviously may be incorporated into the partitioned elements, throughappropriate and obvious casting or moulding processes, such that themanifold comprises only three elements.

[0054] It should be noted that manifold 500 is actually two mirror imagemanifolds 500-1,500-2 sharing some common features, for example, cathodeair return from the stacks. Thus, reformate fuel flows from reforWERunit 1100 in two parallel streams to stacks 344 and 346 and is returnedto reforWER 1100 in two parallel streams. Likewise, cathode air flowfrom air supply assembly 900 is divided into two parallel streams andenters into each manifold 500-1,500-2 via mirror image couplings 902-1and 902-2 (FIGS. 8-10 and 13). Fuel cell assembly 400 thus is seen tohave its fuel cell stacks 344,346 connected in series electrically butserviced by gas flows in parallel.

[0055] For simplicity of presentation and discussion, except wherefunctions are unique, the following construction and function isdirected to manifold 500-1 but should be understood to be equallyapplicable to mirror-image manifold 500-2.

[0056] Bottom plate 502 is the base plate for the manifold and forms thebottom for various chambers formed by combination of plate 502 withlower partitioned element 504, defining a lower distribution element505, as shown in FIG. 16. Intermediate plate 506 completes the chambersin element 504 and forms the bottom plate for upper partitioned element508, defining an upper distribution element 509. Top plate 510 completesthe chambers in element 508 and forms the mounting base for fuel cellassembly 300, heat exchangers 600, and reforWER unit 1100, as describedabove.

[0057] In operation, air enters a first bottom chamber 512 via coupling902-1, flows upwards through slots 514-1,514-2,514-3 into heat exchanger600-1, through the heat exchanger conventionally where the air is heatedas described below, downwards through slot 516-3 into a first upperchamber 518, thence through opening 520 in plate 506 into a second lowerchamber 522. In chamber 518, the heated air is controllably mixed withcool air entering the chamber via bypass connection 904-1 from airsupply assembly 900. The tempered air flows upwards from chamber 522through opening 524 in plate 506 into a chamber 526 which defines acathode supply plenum for supplying reaction and cooling air upwardsthrough slotted openings 528 to the cathode air flow passages in stack344. Spent air is returned from the cathodes via slotted openings 530into a cathode return plenum 532 and flows downwards through an opening534 in plate 506 into a common cathode air return runner 536 leadinginto a tail-gas combustor 1102 within reforWER 1100.

[0058] Hot reformate from reforWER 1100 enters manifold 500-1 viaopening 538 in top plate 510 and flows into chamber 540, thencedownwards through opening 542 into a feed runner 544, and upwardsthrough opening 546 into a chamber 548 defining an anode supply plenumfor stack 344.

[0059] Preferably, opening 546 defines a seat for a valve having a ball550 (FIG. 14), preferably held in place by gravity, for allowing flow ofreformate during operation but preventing flow of oxygen into the anodeswhen the system is shut down. Further, preferably, chamber 544 and/or548 contains an oxygen-reactive material (not shown here but indicatedas 134 in FIG. 2), such as nickel wool, through which reformate mayeasily pass but which can scavenge any oxygen passing by ball 550 on itsway to the anodes.

[0060] Preferably, cathode supply chamber 522 and anode supply chamber544 are configured to maximize the area of the common wall between them,such that chambers 522,544 define a co-flow heat exchanger which tendsto decrease the temperature difference between the cathode supply airand the anode supply reformate.

[0061] From chamber 548, reformate flows upwards through slots 552 intothe anode flow passages in stack 344. Spent reformate (“tail gas”) flowsdownwards through slots 554 into an anode return plenum 556 and thencedownwards through opening 558 into a reformate return runner 560. Fromrunner 560, spent reformate flows upwards through opening 562 intoelongate chamber 564 common with manifold 500-2 and thence throughopenings 566 into the tail-gas combustor 1102 in reforWER 1100.Preferably, opening 562 is also formed as a check valve seat likeopening 546 for receiving a check ball 563 preferably held in place bygravity for preventing reverse flow of oxygen into the anodes when thesystem is shut down. Further, preferably, chamber 556 and/or 560, likechamber 548, contains an oxygen-reactive material (not shown here butindicated as 134 in FIG. 2), such as nickel wool, through which the tailgas may easily pass but which can scavenge any oxygen passing by ball563 on its way to the anodes.

[0062] Burned tail gas from the combustor enters manifold 500-1 via slot568-3 and flows via slots 568-2,568-1 into bottom chamber 570 and thencethrough opening 572 into chamber 574 which acts as a supply plenum forcathode air heat exchanger 600-1. Burned tail gas flows upward fromchamber 574 through openings 576 and through heat exchanger 600-1, thusheating incoming cathode air, returning through openings 578 intochamber 580 and thence via openings 582 into a tempering jacket space354 (FIG. 7) surrounding stack 344 between the fuel cells 311 and cover342. The stack is thus tempered by the exhaust gas. The burned tail gasreturns from jacket 354 via openings 584 into an exhaust plenumcomprising openings 586-3,586-2,586-1 which is vented to the atmosphereby exhaust pipe 588 and pipe flange 590.

[0063] Referring to FIGS. 19 through 22, a reforWER 1100 in accordancewith the system is mounted on the upper surface of plate 510 (FIG. 18)over openings 566 and 568-3 in manifold portions 500-1,500-2, asdescribed below. ReforWER 1100 is generally laid out having a firstportion 1104 for receiving, metering, and mixing liquid fuel and air,for vaporizing the fuel/air mixture, and for passing the vaporizedmixture into a second portion 1106 for partially oxidizing the fuel inthe mixture catalytically and passing the reformed fuel into manifoldassembly 500. Portions 1104,1106 are preferably joined by through bolts1108. Portion 1106 also houses tail gas combustor 1102 as describedbelow.

[0064] For clarity in the following description, the item numbers asoriginally shown in FIG. 2 are used, where appropriate, in FIGS. 19-22in relating the flow paths and controls shown schematically in FIG. 2 tothe actual apparatus shown in FIGS. 19-22; otherwise, numbers relatingto reforWER 700 are in the 7xx series.

[0065] Referring to portion 1104, a fuel injection head 1109 has anaxial bore 1110 for receiving a fuel injector assembly 1112 comprising afuel injector 102 which may be similar to fuel injectors provided onconventional internal combustion engines. Assembly 1112 furthercomprises an annular heat exchanger 1116. Fuel is supplied by fuel pump94 (FIG. 2) to entry fitting 1118 which communicates with exchanger1116, wherein the fuel is preheated, and then is fed by hose 1120 toinjector 102. Preheating of the fuel also acts to cool the fuel injectorand is a first waste energy recovery feature in accordance with theinvention. Fuel is injected periodically, responsive to control system200, into a mixing chamber 1122 adjacent head 1109.

[0066] Air is supplied to reforWER 1100 from air pump 48 via line 74past MAF 78 and through control valve 80, entering via T-fitting 1124(omitted from FIG. 20 for clarity but shown in FIG. 19) wherein the airflow is divided into two portions. A first air flow passes throughcontrol valve 82 and directly into a distribution header 1126 formed inhead 1108 for admission into mixing chamber 1122. A second air flowpasses through feed tube 1128 along the length of reforWER 1100, thencethrough a pre-heat heat exchanger 84 formed in portion 1106 adjacentcombustor 1102, and returns through tube 1132 to header 1126 to beadmitted to mixing chamber 1122. Regulation of control valve 82 controlsair flow through exchanger 84 and hence the average temperature of airentering the mixing chamber. Exchanger 84 is a second waste energyrecovery feature in accordance with the invention.

[0067] In mixing chamber 1122, the injected fuel is vaporized andturbulently mixed with both air portions. The mixed vapor is passedthrough a porous “mixing foam” 1134 into a start combustor chamber 77provided with a mixed vapor ignition means, preferably an igniter 79.Warm-up of system 1000 is shortened by igniting mixed vapor in chamber77, responsive to control system 200, and passing the hot combustionproducts forward directly through the plates in reformer 106 and theanodes in stacks 44,46. Igniter 79 is not used in normal operation atelevated temperature, and a porous flame arrester 1136 preventsflashback from the reformer 106 into chamber 77.

[0068] ReforWER portion 1106 is essentially a plate reformer 106 andheat exchanger encased in a metal enclosure 1107 which sealable mateswith the wall 1109 of chamber 77. Further, portion 1106 preferablyincludes a sturdy bottom plate 1111 for mounting against plate 510 inmanifold 500. Portion 1106 comprises a plurality of preferably identicalreformer plates 1138, each of which is coated on one side, designatedhere for clarity as side A (FIG. 21), with a hydrocarbon-reformingcatalyst. Plates 1138 are coated on opposite side B (FIG. 22) with acatalytic washcoat for reduced CO and hydrocarbon emissions fromcombustor 1102. The plates are stacked in alternating order such thateach side A faces another side A and each side B faces another side B.

[0069] Sides A are separated by sealing reformer spacers 1140 (FIG. 21)such that a reforming space is created between each pair of sides A.Mixed vapor flows across the catalyst on sides A, is reformed toreformate fuel, and passes through reformate ducts 1142 formed bycooperation of the plates and spacers, which ducts engage opening 538 inmanifold 500 (FIG. 13) for conveying reformate to the fuel cell stacksas described above.

[0070] Sides B are separated by sealing combustor spacers 1144 (FIG. 22)such that a combustion exhaust space is created between each pair ofsides B. Spacers 1144 prevent cross-contamination of reformate withexhaust. Tail gas from the anodes in the stacks is fed to combustor 1102from manifold 500 as described above, and is ignited periodically by anigniter 1145 disposed in a head housing 1147 defining an upper end ofcombustor 1102. Exhaust from combustor 1102 flows across sides B,heating plates 1138 from side B and thus enhancing the fuel reformingproceeding on side A, and passes through exhaust ducts 1146 formed bycooperation of the plates and spacers, which ducts engage openings 568-3in manifold 500 (FIG. 13) for conveying combustor exhaust to cathode airheat exchangers 600-1,600-2 as described above. Exchange of combustorheat between sides B and A is a third waste energy recovery feature inaccordance with the invention.

[0071] The plates 1138 and spacers 1140,1144 may be formed easily andinexpensively by stamping from sheet metal of appropriate thermalstability, as is known to those skilled in the metallurgical arts.Preferably, the spacers are then permanently secured to the plates as bywelding or brazing before the reformer is assembled. Alternatively, thespacers may be formed integrally with the plates as by etching from ametal blank having the combined thickness of a plate and spacer.

[0072] Preferably, reforWER 1100 includes a first temperature sensor1148 disposed in chamber 77 for sensing the temperature of mixed vaporentering the reformer; a second temperature sensor 1150 disposed in oneof exhaust ducts 1146 for sensing the temperature of the combustorexhaust after heat loss to the reformer; a third temperature sensor 1152disposed within combustor 1102 for sensing the combustion temperature;and a fourth temperature sensor 1154 disposed in one of reformate ducts1142 for sensing the temperature of reformate leaving the reforming unit1100.

[0073] Thus reforWER 1100 is seen to be an integrated reforming unitcomprising a hydrocarbon fuel reformer; an integral tail gas and cathodeair combustor and reformer heat exchanger; a fuel pre-heater and fuelinjector cooler; a fuel injector and fuel/air mixer and vaporizer; areforming air pre-heater; a reforming air temperature control valve andmeans; and a pre-reformer start-up combustor. The integration of a platereformer, tail gas combustor, and combustor gas heat exchanger allowsfor efficient operation modes of the reformer. Specifically, thereformer may be operated in an endothermic mode (steam reforming, as isknown in the art, but not shown) wherein the combustor gas heatexchanger and combustor provide the energy for the reforming function.In exothermic reforming mode, as discussed herein, the combustor gasheat exchanger aids in the temperature regulation of the reformer andreduces significant thermal gradients in the unit.

[0074] Referring to FIGS. 2, 10, 23, and 24, an air supply system 900for fuel cell system 1000 is shown. As in the reforWER description andfigures above, numbers from FIG. 2 will be used where appropriate;otherwise, elements of system 900 are indicated by 9xx numbers.

[0075] A conventional high speed inlet air pump 48 draws inlet air 50through an air filter 52, past a first MAF sensor 54, through a sonicsilencer 56 which may be a resonance chamber, and through a coolingshroud 58 surrounding pump 48.

[0076] Air output 60 from pump 48, at a pressure sensed by pressuresensor 61, is conveyed via inlet 906 into a manifold block 908 having acentral plenum 910. A first feed from plenum 910 is conveyed ascombustor cooling air 64, via a second MAF sensor 68 and control valve70 disposed in block 908. Cooling air 64 enters manifold 500 via aflexible connector 912 (FIG. 13) and is mixed therein with spent cathodeair in cathode air return 536 (FIG. 16) and passed to combustor 1102 asdescribed above. A second feed from plenum 910 is conveyed as reformerair feed 74 to hydrocarbon fuel vaporizer 76 via a third MAF sensor 78and reformer air control valve 80.

[0077] Cathode air feed 75 from plenum 910 is controlled by cathode aircontrol valve 86, is divided into flows 75-1 and 75-2, and is sent asthe primary cathode air flows to cathode air heat exchangers 600-1,600-2via flexible connectors 902-1,902-2, respectively, as described above.Cathode bypass air feed 87 from plenum 910 is also divided into twoflows 87-1,87-2 and is sent as the bypass cathode air flows via flexibleconnectors 904-1,904-2, respectively, for combination in manifold 500with heated cathode air flows from heat exchangers 600-1,600-2, asdescribed above. Varying the volume of air passing through control valve88 varies the temperature of the cathode air sent to the stacks.

[0078] Integrated air supply system 200 thus provides and controls allthe air flows required in system 1000.

[0079] An SOFC system 1000 in accordance with the invention isespecially useful as an auxiliary power unit (APU) for vehicles 136(FIG. 12) on which the APU may be mounted, such as cars and trucks,boats and ships, and airplanes, wherein motive power is supplied by aconventional engine and the auxiliary electrical power needs are met byan SOFC system.

[0080] An SOFC assembly in accordance with the invention is also usefulas a stationary power plant such as, for example, in a household or forcommercial usage.

[0081] While the invention has been described by reference to variousspecific embodiments, it should be understood that numerous changes maybe made within the spirit and scope of the inventive concepts described.Accordingly, it is intended that the invention not be limited to thedescribed embodiments, but will have full scope defined by the languageof the following claims.

What is claimed is:
 1. A fuel cell system for generating electric powerby combination of oxygen with hydrogen-containing fuel, comprising: a) aplurality of individual fuel cells organized into at least one fuel cellstack assembly including a plurality of cathodes and anodes; b) manifoldmeans having passageways for conveying said fuel and said oxygen in theform of air to said stack assembly and for returning spent cathode airand tail gas fuel from said stack assembly; and c) an integratingreformer unit connected to said manifold means for reforminghydrocarbons to provide said fuel to said stack assembly, said reformerunit including, a mixing chamber for mixing liquid hydrocarbon fuel toform a fuel/air mixture, means for injecting liquid hydrocarbon fuelinto said mixing chamber, means for entering reforming air into saidmixing chamber, a multiple-plate reformer downstream of said mixingchamber for producing reformed hydrocarbon fuel from said vaporizedfuel/air mixture, means for conveying said reformed fuel within saidreformer unit to said manifold, combustor means for receiving andburning tail gas and spent cathode air from said stack assembly via saidmanifold, heat exchanging means between said combustor means and saidreformer, and means for conveying exhaust from said combustor meansthrough said reformer unit and into said manifold means.
 2. A fuel cellsystem in accordance with claim 1 wherein said integrating reformer unitfurther comprises: a) means for tempering said reforming air beingentered into said mixing chamber; and b) heat exchanging means betweensaid combustor means and said reforming air tempering means.
 3. A fuelcell system in accordance with claim 1 wherein said integrating reformerunit further comprises means for vaporizing said fuel/air mixture insaid mixing chamber.
 4. A fuel cell system in accordance with claim 1wherein said integrating reformer unit further comprises a start-upcombustion chamber communicating with said mixing chamber, includingmeans for selectively igniting said fuel air mixture as desired in saidstart-up combustion chamber.
 5. A fuel cell system in accordance withclaim 1 wherein said fuel cells are solid-oxide fuel cells.
 6. A fuelcell system in accordance with claim 1 wherein said fuel injecting meansis a fuel injector.
 7. A fuel cell system in accordance with claim 1wherein said combustor means is disposed within said multiple platereformer.
 8. A fuel cell system in accordance with claim 7 wherein saidmultiple-plate reformer and combustor means includes a plurality ofplates having a reforming catalyst on an A side thereof and having a Bside opposite said A side, said plates being so ordered that A sidesface A sides and B sides face B sides, each plate having a centralopening, a plurality of reformer spacers disposed between said A sidesto space said A sides apart, forming a plurality of slots between said Asides for passage of fuel/mixture into said reformer and passage ofreformate out of said reformer, a plurality of combustor spacersdisposed between said B sides to space said B sides apart, forming aplurality of slots between said B sides for passage of combustor exhaustout of said reformer wherein said spacers and said central openings insaid plurality of plates cooperate to define a combustion chamber withinsaid reformer, said combustion chamber being open to said combustorexhaust slots and closed to said reformer slots, said reformer spacersand said combustor spacers being so configured as to prevent gas flowcommunication of said reformate slots with said combustor exhaust slotswherein said combustor exhaust slots and said reformer slots define ameans for transferring heat through said plates from said combustionexhaust to said reforming catalyst, and means for conveying said spentcathode air and said tail gas fuel from said manifold to said combustionchamber.
 9. A fuel cell system in accordance with claim 8 wherein saidplates and said spacers are stamped from sheet metal.
 10. A fuel cellsystem in accordance with claim 8 wherein said reformer spacers areformed integrally with said plates.
 11. A fuel cell system in accordancewith claim 8 wherein said combustor spacers are formed integrally withsaid plates.
 12. A fuel cell system in accordance with claim 8 furthercomprising means for igniting said spent cathode air and said tail gasfuel in said combustion chamber.
 13. A fuel cell system in accordancewith claim 1 further comprising means for pre-heating said hydrocarbonfuel before injection of said fuel into said mixing chamber.
 14. A fuelcell system in accordance with claim 1 wherein said means for temperingsaid reforming air being entered into said mixing chamber includes aheat exchanger disposed within said multiple plate reformer andcombustor.
 15. A fuel cell system in accordance with claim 14 whereinmeans for tempering further includes an air control valve disposed in aflow path of said air being tempered.
 16. A fuel cell system inaccordance with claim 1 wherein said system is mounted on a vehicle. 17.A fuel cell system in accordance with claim 16 wherein said vehicle isselected from the group consisting of car, truck, boat, and airplane.18. A fuel cell system in accordance with claim 16 wherein said systemis an auxiliary power unit for said vehicle.
 19. An automotive vehicle,comprising a fuel cell system for generating auxiliary power for saidvehicle, said system including a plurality of individual fuel cellsorganized into at least one fuel cell stack assembly including aplurality of cathodes and anodes, manifold means having passageways forconveying said fuel and said oxygen in the form of air to said stackassembly and for returning spent cathode air and tail gas fuel from saidstack assembly, and an integrating reformer unit connected to saidmanifold means for reforming hydrocarbons to provide said fuel to saidstack assembly, wherein said reformer unit includes, a mixing chamberfor mixing liquid hydrocarbon fuel to form a fuel/air mixture, means forinjecting liquid hydrocarbon fuel into said mixing chamber, means forentering reforming air into said mixing chamber, a multiple-platereformer downstream of said mixing chamber for producing reformedhydrocarbon fuel from said vaporized fuel/air mixture, means forconveying said reformed fuel within said reformer unit to said manifold,combustor means for receiving and burning tail gas and spent cathode airreturned from said stack assembly via said manifold, heat exchangingmeans between said combustor means and said reformer, and means forconveying exhaust from said combustor means through said reformer unitand into said manifold means.
 20. An automotive vehicle in accordancewith claim 19 wherein said integrating reformer unit further comprises:means for tempering said reforming air being entered into said mixingchamber, and heat exchanging means between said combustor means and saidreforming air tempering means.
 21. An automotive vehicle in accordancewith claim 19 wherein said integrating reformer unit further comprisesmeans for vaporizing said fuel/air mixture in said mixing chamber. 22.An integrating reformer unit for reforming hydrocarbons to providehydrogen-rich fuel to a fuel cell stack, said reformer unit including, amixing chamber for mixing liquid hydrocarbon fuel to form a fuel/airmixture, means for injecting liquid hydrocarbon fuel into said mixingchamber, means for entering reforming air into said mixing chamber, amultiple-plate reformer downstream of said mixing chamber for producingreformed hydrocarbon fuel from said vaporized fuel/air mixture, meansfor conveying said reformed fuel within said reformer unit to saidmanifold, combustor means for receiving and burning tail gas and spentcathode air from said stack assembly via said manifold, heat exchangingmeans between said combustor means and said reformer, and means forconveying exhaust from said combustor means through said reformer unitand into said manifold means.
 23. An integrating reformer unit inaccordance with claim 22 further comprising: means for tempering saidreforming air being entered into said mixing chamber, and heatexchanging means between said combustor means and said reforming airtempering means.
 24. An integrating reformer unit in accordance withclaim 22 further comprising means for vaporizing said fuel/air mixturein said mixing chamber.